Hip prostheses for replacement of damaged or diseased human hips have long been known in the art. Such prosthetic devices generally comprise an acetabular component providing an artificial acetabulum, a femoral component including a femoral stem for implantation in the femur and a neck portion carrying a head for being rotatably received in the artificial acetabulum. Examples of such devices are disclosed in U.S. Pat. Nos. 4,365,358 and 4,514,865. Generally, the femoral stem of such devices integrally comprises a proximal portion for implantation in the proximal femur and a distal portion which is closely received in the medullary canal so as to extend into the diaphysis or shaft of the femur. Whereas such femoral components are offered in various sizes, difficulty can still be encountered in achieving a proper seating of the femoral stem in the femur. In this regard, where a femoral component is selected having a proximal portion appropriately sized for the proximal femur, the distal stem may not be of proper cross-sectional diameter for being closely received in the portion of the medullary canal into which it is to be implanted. For example, if the distal portion is too small, the stability of the implant can be undermined, and post surgical pain in the location of the distal stem can result. Accordingly, the femoral components presently known in the art are not interchangeably adaptable to various femur configurations.
Also known in the art is the use of femoral stems having porous exterior surface portions which receive bone ingrowth from the femur and thereby are secured in the femur. Whereas bone ingrowth is one of the preferred means of securing such femoral implants, femoral stems so implanted are very difficult to remove should replacement of the prosthesis be required. The general removal procedure involves the use of an osteotome to chisel the bone away from the porous surface and then the extraction of the femoral stem from the femur. However, this is a difficult procedure which can be highly destructive of the bone tissue of the proximal femur.
Therefore, it is an object of the present invention to provide an improved femoral component for a hip prosthesis.
It is another object of the present invention to provide an improved femoral component including a femoral stem having a proximal portion which releasably engages a cooperating distal portion such that the proximal and distal portions of the stem can be independently sized.
A further object of the present invention is to provide an improved femoral component which can feature a porous surface portion for being secured by bone ingrowth from the femur, yet is more easily removed for replacement.
Yet another object of the present invention is to provide an inventory of components which are inexpensive to manufacture and easy to implant.